T4 but not T3 administration is associated with increased recurrence of Graves' disease after successful medical therapy

TSH has been incriminated in Graves' disease for increasing the production of antibodies against TSH receptor (TRAb). It has been, therefore, suggested that T-4 administration after successful antithyroid drug (ATD) treatment may indirectly decrease the production of TRAb and, therefore, the frequency of recurrence of hyperthyroidism. To study the role of T-4 and T-3 on the recurrence rate of Graves' disease 108 patients with Graves' disease (22 males, age: 49.8+/-14.3 yr, mean+/-SD, and 86 females, age: 41.7+/-12 yr) were followed-up for 24 months after successful treatment with ATD (carbimazole). During the follow-up period, patients daily received either 100 mug T-4 or 25 mug T-3 or placebo after random and double-blinded assignment into three groups. They were evaluated trimonthly up to 12 months and at 24 months. Plasma TRAb levels were measured at the beginning and at 12 months. At 12 months of the follow-up period, 14 out of 33 (42.4%), 6 out of 38 (15.8%), and 9 out of 37 (24.3%) patients receiving T-4, T-3 and placebo, respectively, recurred. Recurrence rate of T-4-treated patients was statistically higher than that of the T-3-treated patients or controls (p<0.05). At the beginning of the follow-up period patients who were going to recur had significantly higher TRAb levels and goiter weight than patients who were not (p<0.05). At 24 months of the follow-up period, from the patients who did not drop out of the study, none out of 11 (0%), 2 out of 19 (10.5%) and 1 out of 12 (8.3%) receiving T-4, T-3 and placebo, respectively, recurred. We conclude that T-4 administration after successful ATD treatment of Graves' disease is associated with increased recurrence of hyperthyroidism as compared to the T-3 or placebo administration. High TRAb levels and goiter weight at the end of ATD treatment may hint at recurrence. (C) 2003, Editrice Kurtis.